The present invention relates to a transmission type display device and a method for controlling its display colors. To be more specific, the present invention relates to a transmission type display device which displays color images with plural light sources having different emission colors and which can control display chromaticity and maintain desired display chromaticity, and also relates to a method for controlling the display colors.
A transmission type display device composed of light sources having different emission colors enables white color (color temperature) to be displayed as white by changing the emission intensity of each light source.
This transmission type display device has less gradation deterioration, compared, for example, with a display device which calculates and corrects the numerical values of image data. This transmission type display device also offers a display with higher color purity by using light sources whose emission spectrums are narrow, such as a light-emitting diode (LED).
However, in such a transmission type display device, the chromaticity of display images changes as the emission intensity or emission spectrum of each color light source changes due to temperature or time. To reduce this change, it is necessary to adjust the emission intensity of each color light source by using a chromaticity sensor.
The chromaticity sensor used here preferably has a luminosity (spectral) characteristics (isochromat function: x(λ), y(λ), z(λ)) proposed by CIE1931 (published by International Commission on Illumination).
However, it is difficult to produce a sensor having this characteristic with high precision, so those sensors used in color luminosity meters contain various ideas (Please see Japanese Unexamined Patent Publication No. 49765/1997). Consequently, these sensors are too expensive to be provided in each display device. Installing such a sensor on the display surface of a display device disturbs the actual use of the display device, so it is generally preferable to install it not on the display surface but inside the display surface toward the light source side. Installing the sensor inside the display device means that no correction is applied to the spectral transmittance characteristics of the shutter part, which makes the colors actually displayed different from the colors detected by the sensor, because the transmittance characteristics of the shutter part is not constant throughout the whole wavelength of the visible light. This causes a problem that, however precisely the chromaticity sensor may be controlled, display colors change as the emission intensity or colors of the light sources changes.